Abstract:We present a motivated construction of large graphs not containing a given complete bipartite subgraph. The key insight is that the algebraic constructions yield very non-smooth probability distributions.
“…That is, the events are independent. This observation is again due to Bukh and corresponds to Lemma of his paper , though we state and prove it in greater generality. Lemma Suppose and .…”
Section: Preliminariesmentioning
confidence: 54%
“…We will now determine the probability that a randomly chosen polynomial from P d passes through a given set of points. For one point, the probability is 1/q, as shown by the following simple result of Bukh [6]. We include the proof for completeness.…”
Section: Preliminariesmentioning
confidence: 82%
“…The final ingredient we require is again essentially due to Bukh and says that if is a variety which is defined over , then there is a finite collection of absolutely irreducible varieties , each of which is defined over , such that . Since it is less standard than the previous two lemmas, we include the proof.…”
Section: Preliminariesmentioning
confidence: 99%
“…If were equal to , we could apply Lemma from to show that is either bounded by a constant or quite large and then use the corollary of Markov's inequality proved above to show that there are very few pairs for which is large. Unfortunately, may contain degenerate walks as well as the paths we are interested in, so we must somehow take these into account.…”
Section: The Constructionmentioning
confidence: 99%
“…Very recently, Bukh found a simple, elegant method for showing that the Kővári–Sós–Turán bound is tight for sufficiently large in terms of , fusing the algebraic techniques used in all previous constructions with an application of the probabilistic method. In this paper, we adapt his method to make progress on an equally stubborn problem.…”
We use a variant of Bukh's random algebraic method to show that for every natural number k⩾2 there exists a natural number ℓ such that, for every n, there is a graph with n vertices and normalΩkfalse(n1+1/kfalse) edges with at most ℓ paths of length k between any two vertices. A result of Faudree and Simonovits shows that the bound on the number of edges is tight up to the implied constant.
“…That is, the events are independent. This observation is again due to Bukh and corresponds to Lemma of his paper , though we state and prove it in greater generality. Lemma Suppose and .…”
Section: Preliminariesmentioning
confidence: 54%
“…We will now determine the probability that a randomly chosen polynomial from P d passes through a given set of points. For one point, the probability is 1/q, as shown by the following simple result of Bukh [6]. We include the proof for completeness.…”
Section: Preliminariesmentioning
confidence: 82%
“…The final ingredient we require is again essentially due to Bukh and says that if is a variety which is defined over , then there is a finite collection of absolutely irreducible varieties , each of which is defined over , such that . Since it is less standard than the previous two lemmas, we include the proof.…”
Section: Preliminariesmentioning
confidence: 99%
“…If were equal to , we could apply Lemma from to show that is either bounded by a constant or quite large and then use the corollary of Markov's inequality proved above to show that there are very few pairs for which is large. Unfortunately, may contain degenerate walks as well as the paths we are interested in, so we must somehow take these into account.…”
Section: The Constructionmentioning
confidence: 99%
“…Very recently, Bukh found a simple, elegant method for showing that the Kővári–Sós–Turán bound is tight for sufficiently large in terms of , fusing the algebraic techniques used in all previous constructions with an application of the probabilistic method. In this paper, we adapt his method to make progress on an equally stubborn problem.…”
We use a variant of Bukh's random algebraic method to show that for every natural number k⩾2 there exists a natural number ℓ such that, for every n, there is a graph with n vertices and normalΩkfalse(n1+1/kfalse) edges with at most ℓ paths of length k between any two vertices. A result of Faudree and Simonovits shows that the bound on the number of edges is tight up to the implied constant.
Bukh and Conlon used random polynomial graphs to give effective lower bounds on , where is the th power of a balanced rooted tree . We extend their result to give effective lower bounds on , which is the maximum number of edges in a ‐free subgraph of the random graph . Analogous bounds for generalized Turán numbers in random graphs are also proven.
For graphs H, F and integer n, the generalized Turán number ex(n, H, F) denotes the maximum number of copies of H that an F-free n-vertex graph can have. We study this parameter when both H and F are complete bipartite graphs.
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